The present invention relates to a commutator for a rotor, and more particularly, to a commutator preferably used in an electro-drive type fuel pump.
A known electro-drive type fuel pump for an in-tank system is installed in a fuel tank. In such an electro-drive type fuel pump of an in-tank system, a commutator formed of copper, silver, etc., is used. However, if such a commutator is used in a mixed fuel system containing alcohol, it may react with the fuel and may corrode, and deterioration thereof is accelerated.
Therefore, a commutator made of carbon has been proposed. Carbon has better corrosion-resisting properties and a long service life. Because carbon has self-lubricating properties, satisfactory operation with brushes can be achieved. FIG. 2 is a plan view showing one example of a flat type commutator that is formed of carbon and FIG. 3 is a perspective view thereof. As shown in FIGS. 2 and 3, the flat type commutator comprises a plurality of radially disposed segments 31 that have a generally fan-shaped configuration, conductive members 32, each electrically connected to the respective segments 31 and formed from a conductive material such as copper, and an insulative resin-made substrate 30 for supporting the segments 31 and the conductive members 32.
Each of the segments 31 is formed by compressing and molding carbon powder and by thermally treating the segments 31. Further, a hook 33 that connects a coil of an armature 7 is formed on the conductive members 32. The resin-made substrate 30 is formed at the center of the axis of rotation of the segments 31. An axial hole 35, into which the armature (rotor) shaft of a motor is fitted, is formed in the resin-made substrate 30 at the center axis of rotation. Each of the segments 31 and conductive members 32 are insulated from other segments 31 and conductive members 32 by slits 34 formed in the radial direction.
A method for producing such a commutator made of carbon is disclosed in U.S. Pat. Ser. No. 5,175,463. In this fabrication method, the surface of a ring-like carbon member having a parallel surface is first treated so that a metallic ring may be joined thereto. This metallic ring is made of a conductive material, such as copper, and is attached to the surface of the ring-like carbon member by soldering. The commutator is filled with resin to form a resin substrate that supports the carbon member and the metallic ring. Slits 34 are then formed in the carbon member and the metallic ring in the radial direction in order to divide the carbon member and the metallic ring into sections, so that the segments 31 and the conductive members 32 are formed. Subsequently, an armature (rotor) coil is connected to the conductive member 32 by soldering or welding.
In this fabrication method, because the carbon member and the metallic ring are joined together by soldering, the solder can sometimes melt, due to the heat that is necessary to connect the coil, whether by soldering or welding, to the conductive members that are formed by dividing the metallic ring. The bonding strength between the segments, which are created by dividing the carbon member and the conductive member, decreases as the solder melts. Thus, the segments may separate from the conductive member, and conductivity may be diminished.
It is, accordingly, an object of the invention to prevent the bonding strength between the carbon member and the conductive member from decreasing and to improve conductivity by reducing differences in the thermal expansion coefficients between the conductive member and the segments, even though heat is utilized to connect a coil to the conductive members, and by improving the bonding strength between the segments and the conductive members.
With the invention, the segments (carbon member) and the conductive member (metallic ring) are brazed together with a brazing material that does not melt from the heat applied when connecting the coil to the conductive member. For example, a brazing material including nickel and chromium may be used as the brazing material. Thus, the heat generated in connecting the coil to the conductive member does not melt the brazing material.
The contact area between the segments and the conductive members also is decreased. Further, the firing temperature of the segments is higher than the melting point of the brazing material, so as to prevent the segments from cracking when cooling the brazing material.
The present invention will be better understood by reading the description of preferred embodiments described below with reference to the accompanying drawings or reading the scope of claims.